1. Field of the Invention
This invention relates generally to an evaporator for use with a refrigerator and the like, and more particularly to an evaporator for the freezing chamber of a refrigerator, freezing refrigerator or similar apparatus wherein a part of the cooler is provided with a very low temperature portion.
2. Description of the Prior Art
In the art of manufacture of such type of evaporators, there have been mainly employed two different sorts of techniques, i.e., a pipe-on-sheet method and a roll-bond method. An example of an evaporator of the type manufactured with the pipe-on-sheet method is shown in U.S. Pat. No. 4,227,379, the disclosure of which is hereby incorporated by reference. This type of evaporator comprises a refrigerant passage pipe or evaporator coil which extends in a meandering fashion and is fixed, with an adhesive or by other means, to one surface of a sheet of aluminum or other materials. This sheet with the pipe fixed thereto is bent to form a wall or walls to define a freezing chamber of rectangular cross section. The pipe has a passage through which refrigerant flows in gas and liquid phases. However, the evaporator with such construction having a very small number of, usually one or two, pipes designed as refrigerant passageway means, is disadvantageous when a large magnitude of thermal load is applied to a limited portion of the pipe. More specifically, when foodstuff articles of room or normal temperature are placed on an area covering a limited part of the pipe, the portion of the refrigerant within said limited part of the pipe changes from a liquid to a vapor at a very high rate whereby the refrigerant becomes unable to afford to flow, or in more detail, a majority portion of the refrigerant in a portion of the pipe on the outlet side is forced by a pressure of vaporous refrigerant developed in said limited part and thus forcibly discharged out of the pipe while remaining in liquid phase (i.e., while maintaining its cooling energy). This phenomenon will cause to decrease the cooling efficiency of the cooling system as a whole. There is recognized another disadvantage of the evaporator having the above construction that such forced discharge of liquid refrigerant out of the pipe and the resultant flowing of the liquid refrigerant into the suction pipe of a compressor will necessitate the provision of an accumulator at a point within the length of the suction pipe in order to prevent the entry of liquid refrigerant into the compressor. This requirement will complicate the construction of the refrigerating system as a whole and thereby increase the manufacturing cost thereof. A further disadvantage of the pipe-on-sheet type of evaporator wherein the refrigerant passageway means is constituted by one or two pipes, is that the flow resistance of the entire passageway means tends to be high and accordingly the required power consumption by the compressor is increased. The evaporator has a still further disadvantage in the manufacturing process. To be more specific, modifications of a path pattern of the pipe (path along which the pipe extends) require changes in dimensions of the pipe used. In other words, to provide a variety of evaporators of different path patterns of a pipe or pipes, the corresponding kinds of pipes must be prepared thereby creating the need of cumbersome control of pipe stock, complicating the process for assembling the evaporators, and consequently pushing up the overall manufacturing cost.
On the other hand, the so-called "roll-bond" evaporators are manufactured by roll-welding, for example, two superposed aluminum sheets with a tube between them and then expanding or inflating the compressed tube by applying a fluid pressure so as to form a refrigerant passage between the welded sheets. Due to the nature of such process, this passage can not have a sufficiently large cross section and is therefore limited in volume. This volume limitation causes shortcomings such as a low cooling efficiency and a high flow resistance of the evaporator, and those shortcomings lead to a large power consumption by the compressor in the system.